The overall objective of this laboratory is to develop an effective post-transplant treatment regimen which will be applicable to human incompatible organ transplantation to specifically reduce alloimmune responsiveness and permit lowering of immunosuppressive drug dose requirements. The proposed studies utilize a primate renal transplant model and a posttransplant treatment protocol which results in long term tolerance of unrelated RhLA and MLR incompatible rhesus monkey renal allografts. In this model a brief post-transplant course of antithymocyte globulin and infusion of donor bone marrow (DBM) induces specific allogeneic unresponsiveness in a high percentage of recipients without chronic immunosuppressive treatment. The research plan proposes to identify the DBM cell population which promotes tolerance in this model. DBM will be fractionated based on cell surface phenotype before injection into renal allograft recipients and characterized by additional phenotype and functional in vitro studies. Cryopreservation of DBM will be studied to develop a method of ex vivo storage of DBM without loss of activity. The potential synergistic effect of low dose immunosuppressive agents Cyclosporine, Azathioprine and Prednisone in this model will be examined. The significance of RhLA DR antigen matching and pretransplant one way MLR patterns will be analyzed. The specificity of allogeneic unresponsiveness will be determined in skin and kidney retransplantation studies, and the frequency of chimerism will be documented. Analysis of immunoregulatory mechanisms will involve in vitro studies of suppressor cells mediating specific unresponsiveness and in vivo studies with pharmacologic modification of the recipient. Mononuclear cells in long surviving kidney allografts will be isolated RhLA typed, and examined for phenotypic and functional properties. The study of mechanisms and factors involved in development of specific allogeneic unresponsiveness in this outbred primate kidney transplant model may enhance our understanding of incompatible allograft acceptance and lead to a better immunosuppressive therapeutic approach for organ transplantation.